1. Field of the Invention
This invention relates to the preparation of predominantly noncyclic polyalkylene polyamine products and more particularly pertains to a liquid phase catalytic process for synthesizing predominantly noncyclic poly(n-alkylene amines) with low heterocyclic amine content.
2. Prior Art
Heretofore, polyalkylene polyamine compounds and particularly polyethylene polyamine compounds such as diethylenetriamine, triethylenetriamine, and the higher homologs as well as the related carbon-substituted homologs have been conventionally produced by reacting an alkyl halide, e.g. ethylene dichloride, with an amine compound such as ammonia, ethylenediamine, and the like at elevated temperatures and pressures. Generally speaking, relatively high yields of predominantly noncyclic polyethylene polyamine compounds are obtained along with varying yields of heterocyclic amines, e.g. piperazine materials. These processes, while generally employed throughout the industry, suffer from serious disadvantages.
Exemplary shortcomings of these procedures include large amounts of energy required to produce reactants and expensive recovery procedures. The resultant hydrohalide salts of ammonia and the polyamines must undergo caustic neutralization to obtain the free polyamines. Separation of the desired free polyamines is difficult and disposal of the polluting by-products, such as the alkali metal halide salt, is expensive. Additionally, the products produced possess undesirable colorants, limiting use of the material in colorcritical applications.
There are several procedures described in the literature for directly preparing predominantly non-cyclic polyethylene polyamines by the condensation reaction of an aminoalkanol compound and an alkylatable amine compound which do not require neutralization of the reaction product to obtain the desired salt-free polyamines.
For example, U.S. Pat. No. 3,714,259 to Lichtenwalter et al describes a catalytic process for the preparation of lower polyethylene polyamines such as diethylenetriamine, whereby an ethyleneamine compound and an ethanolamine compound are contacted in the presence of hydrogen and a hydrogenation catalyst comprised of oxides of nickel, copper, chromium, and like metals, in liquid phase at a temperature of 140.degree. C. to 170.degree. C. This procedure produces only lower polyethylene polyamines. In addition, the reaction requires extended reaction times to provide acceptable conversions. Yet, when the process is carried out under conditions which provide an acceptable conversion rate, selectivity is sacrificed with attendant production of byproducts such as piperazine and piperazine products. The resulting amine product also contains considerable hydroxyl content, another disadvantage.
Another example of a process of this type is disclosed in U.S. Pat. No. 3,121,115 to Meuly. Here certain phosphoric compounds are disclosed effective as catalysts promoting condensation reactions between several types of amines and aminoalkanols generally. The reaction conditions are relatively mild with the process more specifically involving aminoalkylating certain amines having a replaceable amino hydrogen, particularly aromatic primary and secondary amines with an N-tertiary aminoalkanol. The reactants are heated at from 150.degree. C. to 250.degree. C. in liquid phase with continuous water removal in the presence of a phosphoric acid compound. The disclosed process generally requires long reaction times. It is also limited to the use of a N-tertiary aminoalkanol.
Recent greatly improved processes of this type are also disclosed in U.S. Pat. Nos. 4,036,881 and 4,044,053. Here polyalkylene polyamine compounds are made using phosphorus catalysts. By utilizing these processes mixed products having higher non-cyclic concentrations of product are found than heretofore available via prior art processes.
However, it would be a further advantage in the art to discover a process of making polyalkylene polyamines wherein the product amines contained even a higher concentration of non-cyclic compound than found in the prior art discussed above or other previously disclosed processes. Such advantage coupled with the ability to effect the process at relatively high temperatures would be a distinct advantage in the art.
We have now discovered an improved catalytic process whereby predominantly noncyclic polyalkylene polyamines and preferably poly(n-alkylene polyamines) may be produced from the condensation of an alkanolamine compound with an alkyleneamine compound under economically feasible short reaction times. The improved process provides conversion rates of reactants and selectivity comparable to or higher than those obtained by conventional processes which require neutralization with alkali, as described hereinbefore. A great advantage of the process lies in its ability to produce products having a higher concentration of noncyclic products than heretofore could be achieved. Surprisingly, it has been discovered that the condensation reaction may be carried out under rather severe processing conditions, such as temperature above about 250.degree. C. in liquid phase without any decomposition of the catalyst involved here or products.